[Cutaneo-muscular reflexes of the human hand. I. Methodologic principles].

Cutaneo-muscular reflexes of the human hand were investigated with special regard to methodological characteristics. The reflexes were elicited by electrical stimulation of either the volar side of the index finger or the median nerve at the wrist, they were in both cases recorded from the abductor pollicis brevis muscle. Independent from the stimulus site, the reflex pattern consisted of four inhibitory and excitatory components (I1-E1-I2-E2): an H reflex was recorded from exclusively with median nerve stimulation. With increasing stimulus efficiency (stimulus strength or duration), the components I1, I2, and E2 were enhanced whereas the presumably transcortically mediated E1 component was successively attenuated. Systematic variation of the stimulus interval, in contrast, induced attenuation of I2 and slight enhancement of I1 only at short intervals (750 ms). Comparison of the reflex responses on both sides revealed a distinct asymmetry particularly of the amplitudes and--less distinct--of the latencies. Asymmetries of the E1 component should therefore be interpreted as pathologic only cautiously.